William L. Holcomb

An odd measure of risk: use and misuse of the odds ratio

OBJECTIVE To determine how often the odds ratio, as used in clinical research of obstetrics and gynecology, differs substantially from the risk ratio estimate and to assess whether the difference in these measures leads to misinterpretation of research results. METHODS Articles from 1998 through 1999 in Obstetrics & Gynecology and the American Journal of Obstetrics and Gynecology were searched for the term “odds ratio.” The key odds ratio in each article was identified, and, when possible, an estimated risk ratio was calculated. The odds ratios and the estimated risk ratios were compared quantitatively and graphically. RESULTS Of 151 studies using odds ratios, 107 were suitable to estimate a risk ratio. The difference between the odds ratio and the estimated risk ratio was greater than 20% in 47 (44%) of these articles. An odds ratio appears to magnify an effect compared with a risk ratio. In 39 (26%) articles the odds ratio was interpreted as a risk ratio without explicit justification. CONCLUSION The odds ratio is frequently used, and often misinterpreted, in the current literature of obstetrics and gynecology.

Tocolysis with advanced cervical dilatation.

Objective To assess the feasibility and potential benefit of delaying delivery in women with advanced preterm labor. Methods Two hundred fifty-seven gravidas with intact membranes and preterm labor at cervical dilatations of at least 3 cm were studied. Women were excluded if they had premature rupture of membranes, gestational age less than 24 or more than 35.9 weeks, complete cervical dilatation, severe hemorrhage, chorioamnionitis, and triplets or higher-order gestations. Management consisted of tocolysis with intravenous magnesium sulfate as the primary agent, antenatal steroids, antibiotics, and amniocentesis. The primary endpoint was delay to delivery interval. Statistical analyses by cervical dilatation were performed using the Pearson χ2 test and a nonparametric test of trend. Results Eighty-one percent of pregnancies were referrals in utero from outlying hospitals. Delivery was delayed 24 hours or longer in 74% and beyond 48 hours in 60% of cases. Among 229 women who delivered at our center, 21% remained undelivered after 1 week. Evaluating delay as a function of cervical dilatation, trend analysis found a highly significant inverse relationship (P < .001). Among women dilated 5 cm, 46% delivered beyond 48 hours. Among those dilated 6 cm or more, 19% delivered beyond 48 hours. Mild pulmonary edema developed in five percent, and all responded promptly to medical interventions. Chorioamnionitis developed in eight percent. Conclusion Delaying delivery 24–48 hours to allow antenatal steroid use or other interventions is possible in women with advanced preterm labor.

Body Mass Index Change Between Pregnancies and Small for Gestational Age Births

OBJECTIVE: To estimate whether maternal weight changes between pregnancies influence the risk for small for gestational age (SGA) births. METHODS: SGA cases (n = 8,062) below the tenth percentile birth weight for gestational age were selected from liveborn singletons born of Missouri residents during 1989–1997. Normal weight controls (n = 8,062) were selected according to birth year. The risk of SGA from interpregnancy body mass index (BMI) change and other maternal factors was estimated using logistic regression analysis. RESULTS: An increase in BMI between pregnancies decreased SGA risk (adjusted odds ratio = 0.8; 95% confidence interval 0.7, 1.0). Other risk factors were prior SGA (4.4; 4.0, 4.8), preeclampsia/eclampsia (2.6; 2.1, 3.2), maternal cardiac disease (1.8; 1.1, 2.9), inadequate weight gain (1.9; 1.8, 2.2), and cigarette smoking (1.9; 1.7, 2.3 for 1–9 cigarettes per day; 2.5; 2.2, 2.8 for 10–19/d; and 2.8; 2.5, 3.3 for 20/d or more). CONCLUSION: Increase in interpregnancy BMI lowers SGA risk, but adequate weight gain during pregnancy is more effective. LEVEL OF EVIDENCE: II-2

Abdominal circumference vs. estimated weight to predict large for gestational age birth weight in diabetic pregnancy

Early third trimester fetal abdominal circumference and sonographic fetal weight estimates were compared to predict large for gestational age birth weight in diabetic pregnancy. Both parameters have similar sensitivity, specificity, and predictive values. However, the optimal percentile cutoff values differ. Choice of birth weight standard significantly influences test characteristics. Negative prediction of large birth weight is more accurate than positive prediction. At third trimester sonography with maternal diabetes, the abdominal circumference percentile is potentially useful and should be routinely reported.

The neonatal bisacromial diameter : a prenatal sonographic evaluation

This study was designed to determine which fetal ultrasonographic parameter best correlates with the neonatal bisacromial diameter (BAD). The latter is defined as the distance between the two acromions of the scapulae. The study population included fifty-four uncomplicated singleton pregnant patients whose infants with birth weights of more than 3000 grams were delivered within a week of ultrasound examinations. Six fetal biometric parameters: circumferences of the chest, abdomen, head, arm, and thigh, and estimated fetal weight were obtained by ultrasonography and were compared with the BAD. The best predictor of the neonatal bisacromial diameter was the fetal chest circumference (r = 0.67, p = 0.003) followed by the arm circumference, (r = 0.59, p = 0.03). The fetal chest circumference correlates well with the neonatal shoulder girth as reflected by the neonatal bisacromial diameter.

The effect of cerclage in twin gestations with short cervix: a Bayesian evaluation.

Abstract Objective: Bayesian inference allows the revision of prior clinical estimates of treatment effectiveness based on current data. We apply it to a published dataset evaluating the effect of cerclage upon preterm delivery in twin gestations with a short cervix. Study design: Prior probability distributions for delivery <35 weeks gestation for the control group and the treatment (cerclage) group were constructed under assumptions ranging from treatment having no effect (prior A) to halving early deliveries (prior C). Likelihood functions were calculated based on a published meta-analysis. Posterior probability densities were derived from which risk ratios for early delivery were computed, with 95% credible intervals and the probability of cerclage benefit. Results: Median posterior risk ratios (95% credible intervals) for delivery <35 weeks with cerclage are 1.51 (1.02–2.33) for prior A and 1.11 (0.72–1.77) for prior C. The probability of cerclage benefit ranged from 2.1% for prior A to 31.4% for prior C. By comparison, the conventional risk ratio (95% confidence interval) for early delivery, based on the data alone, is 2.08 (1.18–3.69). Conclusions: As might be anticipated, those with low expectation of cerclage benefit remain more convinced of the ineffectiveness (or harm) of the procedure than those with higher expectations.

Fetal Parvovirus B19 Infection Doppler Studies Allow Noninvasive Treatment of Ascites

Fetal anemia due to marrow suppression from parvovirus B19 infection may lead to fetal hydrops. In cases of hydrops, outcomes include spontaneous resolution, fetal death without intrauterine fetal transfusion, resolution after transfusion, and fetal death after transfusion. Differentiating those who will have spontaneous resolution from those requiring transfusion is problematic and sometimes based on fetal hematologic parameters measured at funicentesis or somewhat subjective sonographic observations. We report a case in which Doppler sonography was used to obviate funicentesis, fetal transfusion, and their attendant risks. High middle cerebral artery (MCA) peak systolic velocity (PSV) is associated with anemia. In this case, improvement from moderate to mild ascites and normal MCA PSV supported the likelihood of spontaneous resolution in progress.

Association of Depression with Complications of Diabetic Pregnancy: A Retrospective Analysis

The goal of this study was to determine whether an association between histories of depression and adverse pregnancy outcome could be established using a retrospective analysis. Participants were a convenience sample of 152 pregnant diabetic women for whom prior pregnancy data were available. Prior pregnancy outcome, depression history, and other clinical characteristics were determined from chart review and medical history questionnaires. Logistic regression was used to determine which of the measured clinical factors, including history of depression, had a significant association with history of pregnancy complications. Thirty-nine patients (26%) had a past history of depression. Three pregnancy complications (preterm labor, pre-eclampsia, fetal prematurity) were more common in the group having a history of depression as was the proportion of participants requiring Caesarean section p( < .05 for each comparison). A history of depression was associated with prior pregnancy complications independent of the effects of parity, prepregnancy BMI, tobacco use history, diabetes type, and presence of diabetes complications (OR = 3.6; 95% CI = 1.5–9.0, p = .006). These retrospective data indicate that depression is linked to complications of diabetic pregnancy and support the need for prospective studies to clarify the effects of depression and its treatment on diabetic pregnancy.